my macbook was working normally after an Apple Tech installed a new upgraded HDD 500 MB 7200 RPM Seagate. About 4 months later it doesn't recognize the HDD, and when I try to boot it with Snow Leopard OS DVD after a long pause, it tells me to reboot, and after I reboot the language selection screen appears, but the pointer is frozen, and doesn't respond. If I remove the HDD the DVD boots normally, and if I reinstall the HDD (without shutting down) it is not seen. I have tested the HDD with a Seagate Test Utility, using a Windows XP laptop, with a USB connection. The drive passes the Drive Short Test, a Generic Short Test (read-write), and the S.T.A.R.T. tests. What could possibly be the problem?